1. Technical Field
The present invention relates to a force detection device and a robot.
2. Related Art
In recent years, industrial robots have been introduced into production facilities such as factories for the purpose of improvement of production efficiency. Such an industrial robot includes an arm that can be driven with respect to one axis or plural axis directions and an end effector such as a hand, an instrument for component inspection, or an instrument for component conveyance attached to the arm distal end side. The industrial robot can execute component manufacturing work such as component assembling work and component machining work, component conveyance work, and component inspection work.
In the industrial robot, a force detection device (a force sensor) is provided between the arm and the end effector. Since the force detection device is provided at the distal end portion of the arm, the weight of the force detection device occupies a part of weight that carried by the robot (a weight capacity). Therefore, the force detection device is desirably light in weight.
JP-A-2013-130433 (Patent Literature 1) describes a force detection device including a first plate, a second plate disposed a predetermined space apart from the first plate and opposed to the first plate, and a sensor element (a piezoelectric element) disposed between the first plate and the second plate. The first plate includes, in the center portion thereof, a first pressing section projecting toward the second plate. The second plate includes, in the center portion thereof, a second pressing section projecting toward the first plate. The sensor element is sandwiched by the first pressing section and the second pressing section. When an external force is applied to at least one of the first plate and the second plate, the sensor element can detect the external force by outputting electric charge corresponding to the external force. The first plate including the first pressing section and the second plate including the second pressing section are integrally formed of stainless steel or the like having a relatively small coefficient of linear expansion. Therefore, it is possible to reduce the influence of thermal expansion of the first plate and the second plate. It is possible to improve detection accuracy of the force detection device.
In the force sensor in the past, a wire is drawn out from the outer circumferential portion of the force sensor (see, for example, JP-A-10-68665 (Patent Literature 2)).
In the force sensor in the past, for communication between the force sensor and the arm of the robot and power supply from the arm to the force sensor, the wire drawn out from the outer circumferential portion of the force sensor is connected to the arm.
However, in the force detection device described in Patent Literature 1, the entire first plate and the entire second plate are formed of the stainless steel. The stainless steel has a small coefficient of linear expansion but has relatively large density. Therefore, the weight of the stainless steel is large.
Note that the detection accuracy of the force detection device has to be maintained high. Therefore, for a reduction in weight, a material having small density cannot simply selected as a material forming the first plate and a material forming the second plate.
In the force sensor described in Patent Literature 2, since the wire is drawn out from the outer circumferential portion of the force sensor, when the arm moves, tension, bend, twist, and the like occur. An unnecessary force is applied to the force sensor. As a result, an error occurs with respect to a force originally desired to be detected and the detection accuracy is deteriorated.